The present invention relates to a vibration pickup with a pressure sleeve.
Vibration pickups of the above mentioned general type are known in the art. One of such vibration pickups with a pressure sleeve is disclosed for example in the German patent document DE 195 24 147.9. It is formed as a knock sensor for monitoring the operation of an internal combustion engine in a motor vehicle. The pressure sleeve is joined through an abutment region fixedly to a component which causes vibrations, for example a motor block of the internal combustion engine.
The vibrations to be detected are knock noises of the internal combustion engine during the operation. They are transmitted through a pressure sleeve to a piezo-ceramic disk as a sensor element with intermediately located contact disks and insulating disks which allow picking up of the signal, so as to form an evaluatable electrical output signal.
This type of mounting or clamping of the sensor element on the pressure sleeve and the mounting of the pressure sleeve on the vibrating component has a great influence on the manufacture. The clamping of the sensor element together with a plurality of individual components, for example with a spring and a seismic mass is performed in the known vibration pickup with a threaded ring which is screwed on the corresponding thread of the pressure sleeve and directly abuts on the seismic mass.
The known threaded ring and thread on the pressure sleeve is a substantial cost factor. In particular, the chips are produced during thread cutting, which can lead after the injection molding of the device to short circuiting. All components must be fixedly compressed in the case of occurring acceleration with definite mechanical pretensioning and retained in this way. When the pretensioning changes, the transmission characteristic line changes and thereby makes the evaluation difficult.
Accordingly, it is an object of the present invention to provide a vibration pickup with a pressure sleeve, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a vibration pickup with a pressure sleeve, in which a substantially ring-shaped spring is held on an outer wall of the pressure sleeve so that the inner periphery of the spring end abuts against the pressure sleeve with at least three regions, directly or indirectly with mechanical tensioning.
When the vibration pickup is designed in accordance with the present invention it has the advantage that it can be produced with relatively simple manufacturing steps and can therefore have a great strength. Since the substantially plate-shaped spring is held at the outer edge of the pressure sleeve by non-circular portion of the inner contour directly or indirectly, the spring abuts against the pressure sleeve on several regions with pretensioning and for example a special threaded ring for mounting of the components of the pressure sleeve can be dispensed with.
In accordance with a preferable embodiment of the present invention, between the spring and the pressure sleeve at least three pins are driven at uniform distances and the inner contour is correspondingly elastically deformed. The pins can have a square or a rectangular and or also a round cross-section. An especially simple insertion of the pin is performed when the pin is wedge shaped and has a cross-section which reduces in direction toward the spring.
In accordance with another advantageous embodiment of the invention, at least three radially inwardly located projections in the substantially ring-shaped spring are held on the outer wall of the pressure sleeve with pretensioning. Projections can be web-shaped and extend in the inner diameter. However, it can be also formed by concave or convex portions which are straight and deviate from the circular inner contour.
An especially reliable holding of the spring on the pressure sleeve is guaranteed when the spring is welded on the projections with the pressure sleeve. Preferably, the welding is performed by a laser welding technique.
In accordance with a preferable embodiment of the invention, the vibration pickup is formed as a knock sensor for vibrations on the motor block of an internal combustion engine in a motor vehicle.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.